X-ray device



w. HOFMANN X-RAY DEVICE Dec. 1 5, 1936.

Filed Feb. 16, 1929 Inventor: Walter Ho'fm arm H is Wfitowney.

Patented Dec. 15, 1936 X-RAY DEVICE Walter Hofmann, Rudolstadt in Thuringia, Germany, assignor to General Electric Company, a corporation of New York Application February 16, 1929,

In Germany February 24,

Serial No. 340,536

3Claims. (01.250 35) frequently caused by auto-electronic discharges due to the fact that inside the evacuated container relatively large metallic bodies which have a high potential difierence, are mounted close to each other.

According to the invention these mentioned disturbances are eliminated-for extensive protection against undesired passing of X-rays towards the outside-by the anti-cathode being installed in a chamber which is opaque to X- rays with the exception of a window through which the X-rays to be used traverse. This chamber is provided with a small window to allow the cathode ray bundle to enter, the latter therefore. being located remote from the anticathode at a place which is nearest to its cathode.

Other objects and features will be apparent as the specification is perused in connection with the accompanying drawing in which Figs. 1, 2 and 3 represent exemplary embodiments of the invention.

Referring to the drawing, the metal ring I is fused with the short inside wall 2 (Fig. 1) of the tubular almost cylindrical hollow glass body 3. This ring I is welded to the pipe 4 which is to be constructed with double walls, in order to provide an opportunity for cooling with liquids, and which is conducting and to be most advantageously made of iron for the sake of easier evacuation. The inside tube 5 is evacuated and sealed at its end, located at the outside of the hollow glass body 3, by means of the fused or welded carrier 6 of the anti-cathode which is to be made of a good heat conducting material (copper or the like). At the other end of this tube 5 which is located approximately in the center of the hollow glass body 3 is installed a circular diaphragm I with an opening 8 of a small diameter (only a few millimeters) which consists of a material which is hard to fuse and not easily penetrated by X-rays (tungsten, tantalu etc.). In the hollow chamber of the double-walled pipe 4, 5 is installed a cylindrical intermediate wall 9 consisting of a material not easily penetrated by X-rays (lead etc.). This intermediate wall 9 is provided with an opening ID for the exit of the useful X-rays which is at the same height as the reflector (target) or the anti-cathode II at the outside of the hollow glass body 3. The intermediate wall 9 has another opening l2 to allow cooling liquidto enter through the inlet conduit l3. This cooling medium occupies the hollow space inside the double-walled pipe 4, 5 which is not 5 taken up by the intermediate wall 9 and flows through the outlet conduit l4.

By this arrangement the secondary electrons emanating from the focal spot are unable to impinge upon and cause radiation from the stem or body of the target or to cause an undesired and harmful charge on the glass walls, since these electrons are neutralized by'the tubes 4, 5, 9 and by the diaphragm 1. Furthermore, since the reflector of" the anti-cathode is separated l from the cooling medium only by a metal wall of negligible thickness, the heat generated at the focal spot is easily conducted away. The parts necessary for the cooling arrangement of the 'X-ray tube, due to the fact that "they are 20 located on the outside of the hollow glass'body, are easily accessible, even more so when the anode is kept at ground potential.

The X-rays possibly passing through the opening 8 are collected by properly designed parts of the cathode arrangement as, for instance, the focusing device l5 which is impenetrable to X- rays at least at the point where these last impinge.

Since it is important for a successful operation of the novel X-ray tube to have the cathode rays emanating from the glow cathode l6 pass through the opening 8 and being directed to the center of the reflector of the anti-cathode II it is advantageous to provide at the anode support or, according to the figure, in the cathode support H, a flexible metal tube I8 as an intermediate part which, in a given case, may be corrugated in order toaccomplish that, when the X-ray tube is manufactured, a corresponding adjustment may be made at the cathode l6 determining the direction of the cathode rays.

To accomplish an effective cooling of the anticathode and all adjacent metal parts it is possible to construct the tube as shown in the embodiment of Fig. 2, viz, in such a way that the intermediate wall 9, opaque to X-rays, is cut off at a certain distance from the anti-cathode and that, in an overlap-ping manner, the outside wall of the 50 double-walled chamber is made opaque to X-rays which can be done, for instance, by covering it with a layer [9 opaque to X-rays. This arrangement has the advantage that all the space in the vicinity of the anti-cathode, inside the chamber 5 between the two Walls may be occupied by the cooling medium.

If, as shown in the embodiments according to Figs. 1 and 2, the place of exit for the useful X-rays is located at the outside of the hollow glass body of the X-ray tube, the new X-ray tube presents the possibility of an especially simple construction and arrangement of protective means against coming in contact with its parts carrying high voltage. For this purpose there may be fastened, as schematically shown in Fig. 3, on a larger scale than the scale of Figs. 1 and 2, any device which may assume any shape which in itself is known to protect against high voltage. The protective device 20 may be designed, for instance, in case the anti-cathode is grounded, so as to have the shape of a closed tube of conducting material. Under certain conditions of operation, it may be desirable to omit the waterjacket and accordingly, in Fig. 3, there is provided a seal between the reentrant portion 2| of the glass envelope and the sealing ring I which is formed directly on the pipe 5. Although the water-cooling arrangement for the tube 5 has been omitted only in Fig. 3 which illustrates also an external shield for the X-ray tube, I wish it to be understood that it may be omitted when such a shield is absent as in the forms illustrated in Figs. 1 and 2..

What I claim as new and desire to secure by Letters Patent of the United States, is:

1. An X-ray device comprising an evacuated envelope which contains an electron-emitting cathode and comprising an anode, means for focusing a discharge upon a spot of restricted area on the anode, means, in addition to the focusing means, and forming a part of the envelope for restraining the discharge from impinging on the anode other than on the said spot of restricted area whereby secondary radiation is precluded, said discharge restraining means comprising a hollow cylinder terminating at one end in the anode and at the end nearer the cathode in a metal plate provided with a relatively small opening for the discharge.

2. An X-ray device comprising an evacuated envelope containing an electron-emitting cathode and an anode, means for focusing a discharge upon a spot of restricted area on the anode, means in addition to the focusing means and forming part of the envelope for restraining the discharge from impinging on the anode other than on the said spot of restricted area whereby secondary radiation is precluded, said discharge restraining means consisting of a member of closed perimeter surrounding the anode and electrically connected thereto and containing material opaque to X-rays, said member comprising a hollow double-walled metal envelope extending toward the cathode and provided at the cathode end with a restricted discharge opening.

3. An X-ray device comprising an evacuated envelope containing an electron-emitting cathode and an anode, means for focusing a discharge upon a spot of restricted area on the anode, means in addition to the focusing means and forming part of the envelope for restraining the discharge from impinging on the anode other than on the said spot of restricted area whereby secondary radiation is precluded, a protective shield surrounding the envelope, said discharge restraining means comprising a hollow cylinder terminated at one end by the anode and at the other end by a metal member provided with a discharge opening, the anode end of said cylinder extending beyond said shield whereby the X-rays emitted by the anode are unobstructed by the shield.

WALTER HOFMANN. 

